The invention relates to an analysis gas-cooling device.
Such devices are used for the cooling of gas samples which are to be analyzed and which are to be kept at a constant temperature for their analysis. This is important, for example, in order to be able to adjust the dew point of the analysis gas, i.e. the temperature at which the partial pressure of the water vapour contained in it is equal to its saturation vapour pressure. For this purpose, the cooling agent of the cooling device is to be kept at a temperature which is to be maintained as exactly constant as possible. This temperature lies typically in the range between 0 and 10xc2x0 C. The regulating increment in the prior art was, for example, +/xe2x88x921.0xc2x0 C. Because the gases to be analyzed are only examined in samples of low volume, the cooling device requires only a low cooling capacity, for example in the range of 100 Watts or less.
The analysis gas is connected to the cooling device by, for example, cooling hoses, which are intended to be kept at a constant temperature by the cooling device, in the manner of a heat exchanger.
To effect the maintaining of a constant temperature, the principle is known of switching a compressor included in the cooling circuit on or off under temperature regulation. By switching the compressor off when a lower limit temperature is reached, the feed of the initially fluidised cooling agent to an evaporator is stopped, so that no further heat extraction can take place due to the change of state of the aggregate of the cooling agent in the evaporator, and the temperature measured at that point rises accordingly. Once an upper limit temperature is reached, the compressor is switched on again, in order to bring about the regulating of the temperature downwards once again, and reducing the temperature of the analysis gas. This incurs a high degree of wear of the compressor, and, in addition, the precision of such a regulating system is low, since even with the compressor switched off there will initially still be cooling agent injected into the evaporator.
The invention is based on the problem of achieving an improvement in this.
The basic philosophy of the invention is to measure the temperature at the cooling device continually or cyclically, and, as a function of fluctuations in relation to a specified reference value, to adjust the inflow of the cooling agent to a conveying device (compressor) for the cooling agent correspondingly.
To achieve this, the invention proposes, in its most general embodiment, an analysis gas-cooling device with a circuit for a cooling agent, whereby the circuit comprises at least one compressor, a liquefier (condenser) downstream of this, and an evaporator for the cooling agent connected to the compressor on the output side, whereby a control element is connected between the output side of the evaporator and the compressor, so as to influence the gas flow conducted from the evaporator to the compressor.
By means of the arrangement according to the invention of a control element between the output side of the evaporator and the compressor, the regulating of the temperature is possible solely by influencing this control element. The compressor, as a conveying device, can continue to run throughout, unaffected by this, without being subjected to the switching procedures which incur wear.
The control element can be incorporated in a control circuit and can be actuated by a temperature as an input parameter, measured at the evaporator. This means that an external influence of the cooling device becomes superfluous, the temperature will automatically be kept constant.
If a valve is used as the control element, a cheap and reliable component is provided which takes charge of the interruption or passing respectively of the gas flow between the evaporator and the compressor.
In this situation, the control element can reduce or shut off the gas flow between the evaporator and the compressor if a lower limit temperature is undercut, and, respectively, if an upper limit temperature is exceeded, it can increase the gas flow between the evaporator and the compressor, up to a maximum value.
Accordingly, the valve can throttle the gas flow in whole or in part, or respectively allow it clear passage.
In order to remove any residual water which may be present in the cooling agent, a drying unit for the cooling agent can be connected upstream of the evaporator.
Further advantages and features can be derived from an embodiment of the object of the invention represented in the drawing and described hereinafter.